1. Field of the Invention
The present invention relates to a liquid crystal apparatus or a driving apparatus using a ferroelectric liquid crystal material and, more particularly, to a liquid crystal apparatus or a driving apparatus which can suppress a flicker generated in a display drive operation at a low temperature.
2. Related Background Art
In a known liquid crystal display element, scanning electrodes and signal electrodes are arranged in a matrix, and a liquid crystal compound is filled between these electrodes to form a large number of pixels so as to display an image or information. As a method of driving the display element, a time-divisional driving method is adopted. In this method, address signals are sequentially, periodically, and selectively applied to the scanning electrodes, and a predetermined information signal is parallelly and selectively applied to the signal electrodes in synchronism with the address signals.
Most of commercially available liquid crystal display elements are TN (Twisted Nematic) liquid crystal described in, e.g., M. Schadt and W. Hellrich, "Voltage Dependent Optical Activity of a Twisted Nematic Liquid Crystal", Applied Physics Letters, 1971, Vol. 18(4), pp. 127 to 128.
In recent years, as an improved conventional liquid crystal element, a liquid crystal element having bistability is proposed in, e.g., Japanese Patent Laid-Open (Kokai) No. 56-107216, U.S. Pat. No. 4,367,924, and the like by Clark and Lagerwall. As a bistable liquid crystal, a ferroelectric liquid crystal having a chiral smectic C phase (SmC*) or H phase (SmH*) is used. In the C or H phase state, the ferroelectric liquid crystal takes a first or second optically stable state in response to an applied electric field, and maintains the state when no electric field is applied. That is, the ferroelectric liquid crystal has bistability, and is expected to be widely used in the field of high-speed storage type display apparatuses having a quick response property with respect to a change in electric field.
The ferroelectric liquid crystal element is driven by driving apparatuses disclosed in, e.g., U.S. Pat. Nos. 4,548,476, 4,655,561, 4,697,887, 4,709,995, 4,712,872, and the like.
However, threshold characteristics of a ferroelectric liquid crystal largely depend on an external temperature, as shown in FIG. 10. More specifically, as a temperature becomes lower, an applied voltage necessary for inversion is increased and a voltage application time is prolonged.
Therefore, a ferroelectric liquid crystal must increase a drive pulse width (scanning selection period) in a driving operation at a low temperature as compared to a scanning driving operation at a frame frequency of 15 Hz at a high temperature. The ferroelectric liquid crystal requires a scanning driving operation at a low frame frequency of, e.g., 5 to 10 Hz. For this reason, in a driving operation at a low temperature, a flicker caused by the scanning driving operation at a low frame frequency occurs.